As an evaporative fuel processing system of a vehicle (e.g., an automobile), a known fuel tank sealing system closes a valve element of a tank sealing valve (a tank closing valve), which is placed between a fuel tank and a canister, to seal the fuel tank (see, for example, JP2013-113401A, which corresponds to US 2013/0134339 A1). This fuel tank sealing system includes the fuel tank, the tank sealing valve, the canister, and a purge control valve and is connected to an intake conduit communicated with a cylinder of an internal combustion engine that drives the vehicle.
The tank sealing valve includes a tank closing solenoid valve of a normally closed type (N/C) having a valve element that is held in a valve closed state except during a part of a driving period of the vehicle or during a fuel refill operation for filling fuel to the fuel tank. Furthermore, in a case where the fuel refill operation is sensed, the valve element of the tank closing solenoid valve is held in a valve open state from the time of sensing the fuel refill operation until an end of the fuel refill operation.
When the valve element of the tank closing solenoid valve is opened at the time of sensing the fuel refill operation, gas, which contains evaporative fuel, can be conducted from the fuel tank to the canister before the time of opening a fuel filler inlet of the vehicle. This is an operation for limiting release of the evaporative fuel from the fuel tank to the atmosphere. In order to effectively execute this operation, an opening operation of the fuel filler inlet needs to be prohibited. Therefore, there exists a waiting time period (a pressure release waiting time period) at the time of executing the fuel refill operation.
Furthermore, a tank interior pressure may be substantially increased during the time period of closing the valve element of the tank closing solenoid valve. In the state where the tank interior pressure is high, when the valve element of the tank closing solenoid valve is opened, a large quantity of the evaporative fuel, which is larger than an adsorbable quantity of the evaporative fuel that can be adsorbed by the canister per unit time, may flow from the fuel tank to the canister. That is, since the large quantity of the evaporative fuel, which exceeds the adsorbable quantity of the evaporative fuel that can be adsorbed by the canister per unit time, instantaneously flows from the fuel tank to the canister, the evaporative fuel, which breaks the canister, may possibly leak to the atmosphere.
Therefore, in the state where the tank interior pressure is relative high, a passing flow quantity of the evaporative fuel, which flows through a passing flow passage in the tank closing solenoid valve, is reduced to limit the leakage of the evaporative fuel from an atmosphere communication hole of the canister to the atmosphere. Furthermore, in a case where the tank interior pressure is relatively low, and thereby there is a no possibility for the evaporative fuel to leak to the atmosphere, it is required to flow a large quantity of the evaporative fuel from the fuel tank to the canister in order to rapidly release the pressure of the fuel tank.
In view of the above points, inventors of the present application have proposed and formed a tank sealing solenoid valve (a comparative example), in which a pressure responsive valve that changes an amount of stroke in response to a pressure of the evaporative fuel, is combined with a tank closing solenoid valve for the purpose of adjusting a flow quantity of the evaporative fuel from the fuel tank to the canister in response to a change in the tank interior pressure (this technique is not a prior art technique).
As shown in FIGS. 4A and 4B, the tank sealing solenoid valve of the comparative example includes a tank closing solenoid valve and a pressure responsive valve.
A first valve element 101 of the tank closing solenoid valve and a second valve element 102 of the pressure responsive valve are axially movably received in a hollow portion, which is formed between a first housing 103 made of synthetic resin and a second housing 104 made of synthetic resin. The first and second housings 103, 104 have a connecting portion, which airtightly connects between the first and second housings 103, 104 by thermal welding (heat welding).
The first and second housings 103, 104 have a first valve chamber 106, a second valve chamber 108, and an outlet port. The evaporative fuel is guided from an inlet port communicated with the fuel tank to the first valve chamber 106 through an inlet flow passage 105. The evaporative fuel is guided from the first valve chamber 106 to the second valve chamber 108 through a valve hole 107. The evaporative fuel is guided from the second valve chamber 108 to the outlet port through an outlet flow passage 110.
The first housing 103 has a first valve seat 111, which is configured into an annular form and is exposed to the first valve chamber 106. The second housing 104 has a second valve seat 112, which is configured into an annular form and is exposed to the second valve chamber 108.
The tank closing solenoid valve includes a solenoid actuator (hereinafter referred to as a solenoid), and a spring. The solenoid generates a magnetic attractive force that magnetically attracts a plunger toward a core upon energization of a coil of the solenoid. The spring urges the first valve element 101 against the first valve seat 111 (toward a first valve element closing side). The first valve element 101 is opened by the solenoid such that the first valve element 101 is lifted from the first valve seat 111 and opens the valve hole 107.
The pressure responsive valve includes a spring 113, which urges the second valve element 102 toward a side away from the second valve seat 112 (toward a second valve element opening side). Furthermore, during the valve opening time of the tank closing solenoid valve, the amount of stroke of the second valve element 102 from the second valve seat 112 is changed by balance between the pressure of the evaporative fuel guided into the second valve chamber 108 and the spring force of the spring 113. Therefore, the passing flow quantity of the evaporative flue is adjusted in response to the change in the amount of stroke of the second valve element 102.
When the plunger is magnetically attracted toward the core upon energization of the coil of the solenoid, the first valve element 101 is moved toward the valve opening side along with the plunger. That is, the first valve element 101 of the tank closing solenoid valve is lifted from the first valve seat 111 to open the valve hole 107.
When the first valve element 101 is opened in this way, the evaporative fuel is guided from the first valve chamber 106 to the second valve chamber 108 through the valve hole 107. At this time, in a case where the pressure of the evaporative fuel, which is guided into the second valve chamber 108, is substantially larger than the spring force of the spring 113, the second valve element 102 pushes the spring 113 to compress the spring 113, so that the second valve element 102 is seated against the second valve seat 112.
In this way, the evaporative fuel, which is guided into the second valve chamber 108, flows to the outlet flow passage 110 through a restriction hole (choking hole) 114 that extends through a center of the second valve element 102. At this time, since the passing flow quantity of the evaporative fuel is limited by the restriction hole 114, a flow quantity of the evaporative fuel, which is conducted from the fuel tank to the canister, becomes a small flow quantity.
Thereafter, when the tank interior pressure is reduced, the pressure of the evaporative fuel, which is guided from the first valve chamber 106 to the second valve chamber 108 through the valve hole 107, is reduced. When the pressure of the evaporative fuel, which is guided from the first valve chamber 106 to the second valve chamber 108 through the valve hole 107, becomes smaller than the spring force of the spring 113, the second valve element 102 is pushed back by the spring force of the spring 113. Therefore, in addition to the evaporative fuel, which passes through the restriction hole 114 toward the outlet flow passage 110, the fuel, which flows on the radially outer side of the second valve element 102 toward the flow passage 110, is added. Thus, the flow quantity of the evaporative fuel, which is guided from the fuel tank to the canister, is changed from the small flow quantity to a large flow quantity.
However, in the tank sealing solenoid valve of the comparative example, a connecting portion of the first housing 103, which receives the first valve element 101 in the first valve chamber 106, and a connecting portion of the second housing 104, which receives the second valve element 102 and the spring 113 in the second valve chamber 108, are abutted and are heat-welded and securely bonded together by a predetermined heat-welding and bonding method.
Therefore, a heat, which is generated at the time of heat-welding and bonding the connecting portion of the first housing 103 and the connecting portion of the second housing 104 together, may deform a valve seat surface of the first valve seat 111, against which the first valve element 101 of the tank closing solenoid valve is seated. Thus, in the case where the valve seat surface of the first valve seat 111 is deformed by the heat, a gas sealing performance of the first valve element 101 relative to the first valve seat 111 may possibly be deteriorated at a full closing time of the tank closing solenoid valve.
Furthermore, the heat, which is generated at the time of heat-welding and boding the connecting portion of the first housing 103 and the connecting portion of the second housing 104 together, may deform a spring seat surface, which holds the end of the spring 113 of the pressure responsive valve. In the case where the spring seat surface, which holds the end of the spring 113 of the pressure responsive valve, is deformed by the heat, the spring force of the spring 113 is changed from a preset value, and thereby flow quantity characteristics of the evaporative fuel relative to a change in the amount of stroke of the second valve element 102 may be varied from product to product.